Package natbib Error: Bibliography not compatible with author-year citations

Question

I have a basic tex file and a bibliography which is exported from Mendeley

However, when I want to cite in the author-year style, I get the error:

Package natbib Error: Bibliography not compatible with author-year citations. (natbib) Press <return> to continue in numerical citation style.

Any clue what's wrong?

Minimum working example:

\documentclass[letterpaper, 10pt]{article}

\usepackage[authoryear]{natbib}
\usepackage{lipsum}

\begin{document}

\lipsum[1-4]
\nocite{*}

\bibliographystyle{apalike}
\bibliography{articles}

\end{document} 

A snippet of my .bib library:

@article{shortcode,
author = {Lastname, Firstname},
file = {:/path/to/file.pdf:pdf},
journal = {Journal name},
number = {xx},
pages = {x--xx},
title = {Title},
volume = {xx},
year = {xxxx}    
}

Answer 1

Another way this error can arise is if one of your BibTeX entries has no year.

Answer 2

When changing the bibliography style, sometimes natbib is upset because it can't interpret the data correctly.

In any case, after changing the argument to \bibliographystyle a run of LaTeX and one of BibTeX are necessary to get back in sync. Removing the .bbl and .aux files before those run is recommended, in order to avoid spurious error messages that might corrupt the .aux file currently being generated.

Answer 3

I had the same error trying to use spmpsci.bst in conjunction with natbib. While natbib's default citation style is author-year, spmpsci.bst is numeric, so this is a strange error to get. I eventually changed the following:

\usepackage[square,sort,comma]{natbib}

to

\usepackage[square,sort,comma,numbers]{natbib}

Problem went away.